Characteristics, extent, and tectonic significance of a middle ordovician back-arc basin in the Southern Appalachian Blue Ridge

A growing body of evidence suggests that a number of Ordovician-aged stratigraphic units in separate lithotectonic belts of the southern Appalachian orogen are genetically related, having formed in a back-arc setting on the Laurentian plate. Research on the Hillabee Greenstone in the Talladega belt and Pumpkinvinve Creek Formation and related bimodal metavolcanic rocks in the Dahlonega Gold belt suggest a similar temporal, spatial, and tectonic origin. Additionally, recent Ordovician isotopic ages for detrital zircons from the Wedowee and Emuckfaw Groups in the Ashland-WedoweeEmuckfaw belt of Alabama (eastern Blue Ridge), as well as stratigraphic correlations of these units with metasedimentary and metavolcanic rocks of the southwestern Dahlonega Gold belt (New Georgia Group) support the idea that the Ashland-Wedowee-Emuckfaw belt and Dahlonega Gold belt should be considered a single lithotectonic terrane. Correlation of the Emuckfaw Group and overlying units (Jackson’s Gap Group) with similar rocks around the southwestern terminus of the Brevard Zone in the Opelika Complex, and farther northeast within the western Inner Piedmont of Georgia and North Carolina (Poor Mountain Formation) indicate that these rocks may also have formed in the same extensive Laurentian plate back-arc basin. Correlations of these units have a significant bearing on interpretations of the tectonic setting for the Taconic orogeny in the southernmost Appalachians, suggesting that it formed as a result of extensional accretionary orogenesis on the overriding (Laurentian) plate, unlike the collisional-style orogenic setting for initial phases of the Taconic in the northern Appalachians.